Polar Antiferromagnets Produced with Orbital Order

Polar states are realized in pseudocubic manganite films fabricated on high-index substrates, in which a Jahn-Teller (JT) distortion remains an active variable. Several types of orbital orders (OOs) were found to develop large optical second harmonics, signaling broken-inversion symmetry distinct from their bulk forms and films on (100) substrates. The observed symmetry lifting and first-principles calculation both indicate that the modified JT q(2) mode drives Mn-site off centering, which can be controlled by a magnetic-field-induced phase transition via a coupling of OO and spin orders.